Media reports suggest that "hookups" (sexual encounters between partners who have no expectation of a romantic commitment) are increasing among adolescents, resulting in unprotected sexual risk behavior, poorer mental health, and increased risk for sexually transmitted disease (STD). However, there have been few scientific investigations of hookups. The majority of studies that have been completed have been descriptive or qualitative and have used varying definitions of hookups;virtually no published research has investigated the predictors and consequences of sexual hookups using a longitudinal design. To address these lacunae in the literature, the proposed program of research will: (1) document the prevalence of penetrative sexual hookups in a representative sample of female adolescents as they transition from high school to college;(2) identify the antecedents of penetrative sexual hookups, including theoretically- and empirically-suggested behavioral risk factors (i.e., alcohol use), person variables, and social-environmental conditions that influence sexual hookups;(3) explore the longitudinal relationship between alcohol use and sexual hookups during acute events and over the first year of college;and (4) evaluate the effects of penetrative sexual hookups on three health outcomes: unwanted sexual experiences/sexual assault, STD incidence, and mental health (e.g., depressive symptoms, self-esteem, psychosomatic symptoms). To achieve these goals, we will recruit 500 female adolescents immediately prior to their first semester in college;at study entry, participants will provide information regarding prior sexual behavior (including hookups) and several hypothesized predictors (e.g., alcohol-related behavior and expectancies, personal characteristics, and social factors) of future hookups. Participants will be contacted monthly over the next year to assess sexual hookups and alcohol use behavior, mental health markers, and experience of unwanted sexual contact;in addition, all participants will be tested for two STDs. The data obtained with this longitudinal design will be analyzed using latent growth curve modeling, which will permit testing of a priori hypotheses regarding the antecedents and consequences of sexual hookups, with special emphasis on the co-occurrence of alcohol use. This study will provide the first large-scale, longitudinal investigation into the physical and mental health consequences of penetrative sex hookups, to inform health promotion and disease prevention efforts for late adolescents. PUBLIC HEALTH RELEVANCE: The proposed research will investigate sexual hookups among young women during the transitional first year of college. We will measure the prevalence of hookups, specify the personal and situational factors that increase the risk of sexual hookups, and explore the mental and physical health consequences of hookups. This research will inform young people, parents, and educators, and facilitate the development of interventions to promote the health of young women.